Skip to Content

What type of light is 400 nm?

Light is a form of electromagnetic radiation that is visible to the human eye. The wavelength of light determines its color and type. Wavelength is measured in nanometers (nm) and different wavelengths fall within different regions of the electromagnetic spectrum. 400 nm falls within the visible violet light spectrum.

The Electromagnetic Spectrum

The electromagnetic spectrum encompasses all types of electromagnetic radiation. It ranges from radio waves with very long wavelengths to gamma rays with very short wavelengths. The visible light portion of the spectrum is just a small sliver within the full range of electromagnetic radiation.

Type Wavelength Range
Radio waves >1 mm
Microwaves 1 mm – 1 m
Infrared 700 nm – 1 mm
Visible light 400 – 700 nm
Ultraviolet 10 – 400 nm
X-rays 0.01 – 10 nm
Gamma rays

As seen in the table, visible light wavelengths range from 400-700 nm. This falls between the infrared and ultraviolet portions of the electromagnetic spectrum.

Visible Light Spectrum

The visible light portion can be further broken down into different colored wavelengths:

Color Wavelength Range
Violet 380-450 nm
Blue 450-495 nm
Green 495-570 nm
Yellow 570-590 nm
Orange 590-620 nm
Red 620-750 nm

The wavelength of 400 nm falls squarely within the violet range of the visible light spectrum. Violet light has wavelengths between approximately 380-450 nm.

Properties of Violet Light

Some key properties of violet light with a 400 nm wavelength:

  • Has a frequency of around 7.50 x 1014 Hz
  • Has an energy of around 3.10 eV per photon
  • Sits at the short wavelength end of the visible spectrum
  • Has a higher frequency and energy than other visible wavelengths
  • Appears as a deep bluish-purple color to the human eye

Violet light with a 400 nm wavelength has one of the shortest wavelengths and highest energies within the visible spectrum. It has a higher frequency than colors like red or orange.

The 400 nm wavelength stimulates receptors in the human eye sensitive to violet hues, causing the brain to perceive it as a bluish-purple color. Many describe it as having a “cooler” tone than longer red/orange wavelengths.

Sources of 400 nm Violet Light

400 nm falls within the nanometer wavelengths that can be produced by LED lighting designed to emit violet photons. Some natural and man-made sources that can produce violet light around 400 nm include:

  • Light-emitting diodes (LEDs)
  • Black lights or UV lamps
  • Mercury vapor lamps
  • Neon lights
  • Argon lasers
  • Some stellar objects like quasars
  • Fluorescence from cosmic rays
  • Aurora borealis

Specialized LED bulbs can be tuned to emit different colors along the visible light spectrum. 400 nm falls within the range that violet LEDs are designed to produce.

Similarly, black lights used for security, fluorescence, and other effects are designed to emit ultraviolet photons right around 400 nm that appear deep violet. Other gas discharge lamps like neon or mercury can also emit some violet wavelengths.

In nature, some stellar phenomena and cosmic radiation can produce trace amounts of light around 400 nm through processes like electron excitation and particle acceleration. This can lead to violet hues in astronomical objects or atmospheric effects like the northern lights.

Uses of 400 nm Violet Light

Some uses and applications that take advantage of 400 nm violet light’s properties:

  • Laser/optical systems – shorter wavelengths can produce smaller focal spots
  • Photolithography – exposing photoresist during semiconductor fabrication
  • Sterilization – high energy per photon has germicidal effects
  • UV curing – rapid polymer cross-linking reactions
  • Spectroscopy – excitation source for fluorescence studies
  • Underwater communications – blue/violet wavelengths transmit further in water
  • Plant growth – stimulates photoreceptors that regulate development
  • Therapy – violet light has some antimicrobial and anti-inflammatory properties
  • Black lights – 400nm UV emissions cause fluorescent glow

The relatively short wavelength of 400 nm violet light allows it to be focused into tighter spots, enabling very precise laser applications. The higher photon energy can induce chemical reactions for UV curing adhesives or photolithography processes.

400 nm also sits in a UVsweet spot” where the light has germicidal properties but is safer than higher energy UV. This makes it useful for sterilization.

Violet light around 400 nm tends to penetrate water better than other visible wavelengths. This makes it useful for underwater lighting or communication applications.

It also has some therapeutic benefits and can stimulate beneficial photoreceptors in plants. And of course, 400 nm UV emissions produce the purple glow closely associated with black lights.

Comparison to Other Wavelengths

400 nm violet light differs from some other common wavelengths in the visible spectrum:

  • 700 nm red light – Lower frequency/energy. Appears as a warmer, redder tone. Better penetration through fog/skin.
  • 550 nm green light – Middle of visible range. Appears as a bright green. Strongly reflected by plants.
  • 470 nm blue light – Higher frequency than red/green. Appears as a cooler, deep blue.

While 700 nm red, 550 nm green, and 470 nm blue are all in the visible range, 400 nm violet has a higher frequency and energy level than all of them. It sits at the very edge of visible wavelengths, right next to the UV portion of the spectrum.

This gives 400 nm light some unique properties compared to red, green and blue – particularly for applications relying on its high photon energy or germicidal effects. But it comes at the cost of poorer penetration through materials.

Violet Light and Human Vision

While 400 nm falls within the visible spectrum, human eyes perceive violet wavelengths differently than other colors:

  • Not sensed strongly by cone cells – violet stimulates S cones minimally
  • Low luminous efficacy – appears dimmer to the human eye
  • Poor acuity – hard to focus violet wavelengths on fovea
  • Less sensitivity – rods are less receptive to short wavelengths

The human eye has lower visual acuity for violet light. The eye’s cone cells, which sense color, are relatively insensitive to short wavelength violet photons compared to other visible colors.

This means violet appears dimmer and is harder to focus on the fovea centralis. The eye’s rod cells also have lower sensitivity to violet relative to other wavelengths.

So while 400 nm light stimulates the eye’s receptors enough to be detected as visible light, human vision is relatively poorer for violet compared to green, yellow, or red wavelengths.


In summary, light with a wavelength of 400 nm falls within the violet region of the electromagnetic spectrum. It has a higher frequency and energy level than other colors in the visible range.

400 nm violet light has a number of scientific and industrial uses due to its short wavelength and germicidal properties. It sits on the border between visible and UV light.

While humans can see it, the eye has lower acuity and sensitivity to 400 nm compared to other visible colors. But its unique properties make violet light around this wavelength useful for many specialized applications.